Secondary battery and electric device

Abstract

The present disclosure relates to a secondary battery and an electric device. The secondary battery comprises a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a lower region and an upper region; the lower region comprises a first negative electrode active material; the upper region comprises a second negative electrode active material; the second negative electrode active material comprises both a carbon material of primary particles and a carbon material of secondary particles; and the volume median diameter Dv50 of the second negative electrode active material is less than or equal to 13 μm.

Description

Secondary batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on Chinese patent application number 202410338654.9, application date March 22, 2024, and invention name “Secondary Battery and Electrical Device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into the present disclosure as a reference. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to secondary batteries and electrical devices. Background Art

[0004] In recent years, with the development of secondary battery technology, it has been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace and other fields.

[0005] Because of the widespread use of secondary batteries, users have also put forward higher requirements on the charging capacity of secondary batteries.

[0006] Summary of the Invention

[0007] The present disclosure is made in view of the above-mentioned problems, and its object is to provide a secondary battery with improved low-temperature fast charging performance and an electric device using the secondary battery.

[0008] In order to achieve the above objectives, the first aspect of the present disclosure provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film formed on at least one surface of the negative electrode current collector; the negative electrode film comprises a lower region and an upper region, the lower region comprises a first negative electrode active material, and the upper region comprises a second negative electrode active material; wherein the second negative electrode active material comprises both primary particles of carbon material and secondary particles of carbon material, and the volume distribution particle size D of the second negative electrode active material is V 50 is less than or equal to 13μm.

[0009] The above technical solution is used in combination by setting two carbon materials (i.e., primary particle carbon material and secondary particle carbon material) in the negative electrode film layer area away from the negative electrode current collector (i.e., the upper area). The granulation structure of the secondary particle carbon material is conducive to reducing the OI value of the material, thereby facilitating low-temperature fast charging performance. At the same time, the single particle carbon material (i.e., primary particle) is conducive to increasing the active specific surface area, reducing the charge transfer resistance (Rct), and further improving the low-temperature fast charging performance of the battery. In addition, by matching different granular carbon materials, the volume distribution particle size D of the second negative electrode active material is madeV 50 is less than or equal to 13μm, so that the upper area of ​​the electrode has a better pore distribution state, which is beneficial to improving the transmission performance of ions and electrons and further improving the low-temperature fast charging performance of the battery.

[0010] In some embodiments, the volume distribution particle size D of the second negative electrode active material is V 50 is 8 μm to 13 μm. The volume distribution particle size D of the second negative electrode active material V 50 Within the above range, it is more conducive to forming a better pore distribution state in the upper area of ​​the electrode, which is more conducive to improving the transmission performance of ions and electrons and improving the low-temperature fast charging performance of the battery.

[0011] In some embodiments, the volume distribution particle size D of the carbon material of the primary particles is V 50 is smaller than the volume distribution particle size D of the carbon material of the secondary particles V 50; Optionally, the volume distribution particle size D of the carbon material of the primary particles V 50 is 3.5 μm to 6 μm, more preferably 3.5 μm to 5.0 μm; optionally, the volume distribution particle size D of the carbon material of the secondary particles V 50 is 10.0 μm to 14.0 μm, and more preferably 10.0 μm to 13.5 μm.

[0012] The above technical solution includes a carbon material with smaller primary particles and a carbon material with larger secondary particles in the negative electrode film layer area away from the negative electrode current collector. The granulation structure in the secondary particle structure with larger particle size is more conducive to reducing the OI value of the material, which is beneficial to the low-temperature fast charging performance; the mixed small-particle primary particle carbon material is more conducive to maintaining a higher active specific surface area, further improving the low-temperature fast charging performance of the battery.

[0013] In some embodiments, the powder OI value of the carbon material of the primary particles is greater than the powder OI value of the carbon material of the secondary particles; optionally, the powder OI value of the carbon material of the primary particles is 3 to 6; optionally, the powder OI value of the carbon material of the secondary particles is 2 to 5.

[0014] In the above technical solution, the OI value of the primary carbon material powder is greater than that of the secondary carbon material powder, which facilitates rapid ion intercalation and deintercalation. Furthermore, by maintaining the OI values ​​of the two carbon material powders within the above range, the material has ion intercalation openings in all directions, allowing it to quickly receive ions, further improving the low-temperature fast-charging performance of the secondary battery.

[0015] In some embodiments, the specific surface area of ​​the carbon material of the primary particles is greater than the specific surface area of ​​the carbon material of the secondary particles; optionally, the specific surface area of ​​the carbon material of the primary particles is 2.0 m 2 / g to 3.5m 2 / g, 2.0m is optional 2 / g to 3.2m 2 / g; Optionally, the specific surface area of ​​the carbon material of the secondary particles is 0.6m 2 / g to 1.5m 2 / g, optional 0.6m 2 / g to 1.2m 2 / g.

[0016] In the above technical solution, the specific surface area of ​​the carbon material of the primary particles is greater than that of the carbon material of the secondary particles, which helps to increase the ratio of active specific surface area, enhance the low-temperature fast-charging performance of the battery, and help reduce side reactions, thereby enabling the battery to achieve both good fast-charging performance and good cycling performance. Furthermore, when the specific surface area of ​​the carbon material is within the corresponding above-mentioned range, it can increase the ion embedding channels in the upper region of the membrane layer, promoting the rapid diffusion of ions from the particle surface to the bulk phase.

[0017] In some embodiments, the carbon material of the primary particles satisfies: the volume distribution particle size D of the carbon material of the primary particles V 10 is 1.0 μm to 3.0 μm.

[0018] In some embodiments, the carbon material of the primary particles satisfies: the volume distribution particle size D of the carbon material of the primary particles V 90 is 9μm to 12μm.

[0019] When the volume distribution particle size Dv10 and / or Dv90 of the carbon material of the primary particles is within the above range, it is beneficial to improve the transport performance of ions and electrons, thereby further improving the fast charging performance of the secondary battery.

[0020] In some embodiments, the carbon material of the primary particles satisfies: the particle size distribution (D V 90-D V 10) / Dv50 is 1.1 to 1.8.

[0021] The particle size distribution of the primary carbon material (D V 90-D V 10) / D V 50 is within this range, indicating that the carbon material of the primary particles is well distributed, which is beneficial for the upper region of the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and further improving the fast charging performance of the secondary battery.

[0022] In some embodiments, the carbon material of the primary particles satisfies: the tap density of the carbon material of the primary particles is 0.8 g / cm 3 to 1.1 g / cm 3 When the tap density is within the above range, the compaction density of the negative electrode film layer can be increased, thereby achieving low-temperature fast charging performance while taking into account the energy density of the battery.

[0023] In some embodiments, the carbon material of the primary particles satisfies the following conditions: the powder compaction density of the carbon material of the primary particles at 20,000 N is 1.35 g / cm 3 Up to 1.55g / cm 3 When the powder compaction density is within the above range, the compaction density of the negative electrode film layer can be increased, thereby achieving low-temperature fast charging performance while taking into account the energy density of the battery.

[0024] In some embodiments, the carbon material of the primary particles satisfies the following conditions: the degree of graphitization of the carbon material of the primary particles is 90% to 93%. When the degree of graphitization of the carbon material of the primary particles is within this range, it is beneficial to improve the ion transport performance of the negative electrode film layer, thereby enabling the secondary battery to achieve both high energy density and good fast charging performance.

[0025] In some embodiments, the carbon material of the secondary particles satisfies: the volume distribution particle size D of the carbon material of the secondary particles V 10 is 4.5μm to 8.0μm.

[0026] In some embodiments, the carbon material of the secondary particles satisfies: the volume distribution particle size D of the carbon material of the secondary particles V 90 is 18μm to 24μm.

[0027] Volume distribution particle size D of secondary particles of carbon material V 10 and / or D V 90 Within this range, it is beneficial for the mutual matching between the carbon material of the secondary particles and the carbon material of the primary particles, thereby being beneficial for the compaction density and further contributing to the energy density of the battery.

[0028] In some embodiments, the carbon material of the secondary particles satisfies: the particle size distribution (D V 90-D V 10) / D V 50 is 0.9 to 1.3. The particle size distribution of the carbon material of the secondary particles (D V 90-D V 10) / D V50 is within this range, indicating that the carbon material is well distributed, which is beneficial for the upper region of the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and further improving the fast charging performance of the secondary battery.

[0029] In some embodiments, the carbon material of the secondary particles satisfies: the tap density of the carbon material of the secondary particles is 0.9 g / cm 3 to 1.2g / cm 3 When the tap density is within the above range, it can cooperate well with the carbon material of the primary particles to increase the compaction density of the negative electrode film layer, thereby improving the low-temperature fast charging performance while taking into account the energy density of the battery.

[0030] In some embodiments, the carbon material of the secondary particles satisfies the following conditions: the powder compaction density of the carbon material of the secondary particles at 20,000 N is 1.55 g / cm 3 to 1.70g / cm 3 When the compaction density of the carbon material powder of the secondary particles is within the above range, it can cooperate well with the carbon material of the primary particles to improve the compaction density of the negative electrode film layer, thereby improving the low-temperature fast charging performance while taking into account the energy density of the battery.

[0031] In some embodiments, the carbon material of the secondary particles satisfies the following conditions: the degree of graphitization of the carbon material of the secondary particles is 92% to 95%, thereby facilitating the secondary battery to have both high energy density and good fast charging performance.

[0032] In some embodiments, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the primary particles is less than the mass proportion of the carbon material of the secondary particles; optionally, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the primary particles is 20% to 40%; optionally, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the secondary particles is 60% to 80%.

[0033] By setting the mass proportion of the carbon material of the primary particles to be smaller than the mass proportion of the carbon material of the secondary particles, it is beneficial to improve the low-temperature fast charging performance of the battery while taking into account the energy density.

[0034] In some embodiments, the carbon material of the primary particles and / or the carbon material of the secondary particles is artificial graphite.

[0035] In some embodiments, the first negative electrode active material includes artificial graphite and / or natural graphite; alternatively, the first negative electrode active material includes both artificial graphite and natural graphite.

[0036] In some embodiments, the first negative electrode active material includes natural graphite, and the volume distribution particle size Dv50 of the natural graphite is 9 μm to 20 μm. The first negative electrode active material includes natural graphite, wherein the abundant coating layer on the surface and the internal pore structure of the natural graphite further enhance low-temperature fast charging performance.

[0037] In some embodiments, the first negative active material includes secondary particles of artificial graphite.

[0038] In some embodiments, the first negative electrode active material comprises artificial graphite, and the volume distribution particle size D of the artificial graphite is V 50 is 12μm to 17μm, optionally 13μm to 16μm.

[0039] In some embodiments, the first negative electrode active material comprises natural graphite. In some embodiments, the volume distribution particle size D of the natural graphite is V 10 is 5.0 μm to 12.0 μm. In some embodiments, the volume distribution particle size D of the natural graphite V 90 is 20 μm to 30 μm. In some embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is 0.9 to 1.3. In some embodiments, the tap density of the natural graphite is 0.9 g / cm 3 to 1.2g / cm 3 In some embodiments, the natural graphite has a powder compaction density of 1.60 g / cm2 at 20,000 N. 3 to 1.90g / cm 3 In some embodiments, the degree of graphitization of the natural graphite is 96% to 98%.

[0040] In some embodiments, the first negative electrode active material comprises artificial graphite. In some embodiments, the volume distribution particle size D of the artificial graphite is V 10 is 4 μm to 8 μm. In some embodiments, the volume distribution particle size D of the artificial graphite is V 90 is 25 μm to 40 μm. In some embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is 1.0 to 1.4. In some embodiments, the tap density of the artificial graphite is 0.95 g / cm 3 Up to 1.25g / cm 3In some embodiments, the powder compaction density of the artificial graphite at 20,000 N is 1.70 g / cm 3 to 1.90g / cm 3 In some embodiments, the degree of graphitization of the artificial graphite is 93% to 95%.

[0041] A second aspect of the present disclosure further provides an electrical device comprising the secondary battery according to the first aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0043] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 1 .

[0044] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0045] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0046] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0047] FIG6 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0048] Description of reference numerals:

[0049] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0050] The following detailed description specifically discloses the embodiments of the secondary battery and the electrical device of the present disclosure. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0051] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0055] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0056] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0057] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0058] In this disclosure, the terms "primary particles" and "secondary particles" have meanings well known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0059] In this disclosure, the volume distribution particle sizes "Dv10," "Dv50," and "Dv90" used in reference to materials have well-known meanings in the art. They represent the particle sizes corresponding to the 10%, 50%, and 90% cumulative volume distribution percentages of the material, respectively. These can be measured using instruments and methods known in the art. For example, measurements can be made using a laser particle size analyzer, as per GB / T 19077-2016. The testing instrument may be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0060] In the present disclosure, the term "powder OI value" has a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray powder diffractometer (X'pert PRO) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain an X-ray diffraction pattern of the powder sample, and the powder OI value of the sample is calculated according to OI value = I004 / I110. Wherein, I004 is the integral area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I110 is the integral area of ​​the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. In the X-ray diffraction analysis test of the present disclosure, a copper target can be used as an anode target, CuKα rays can be used as a radiation source, the ray wavelength scans the 2θ angle range from 20° to 80°, and the scanning rate is 4° / min.

[0061] In this disclosure, the term "specific surface area" has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, the specific surface area can be determined by referring to GB / T 19587-2004, the standard for determining the specific surface area of ​​solid substances by the gas adsorption BET method, using nitrogen adsorption specific surface area analysis and testing methods and calculating the specific surface area using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis and testing can be performed using a Tri Star II 3020 surface and pore analyzer from Micromeritics, USA.

[0062] In this disclosure, the "tap density" referred to in reference to a material has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a powder tap density tester with reference to GB / T5162-2006. The test instrument can be a Dandong Baxter BT-301, and the test parameters are as follows: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, vibration number 5000 times, and a 25mL graduated cylinder.

[0063] In this disclosure, the "compressed density of powder" referred to in the material has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine (such as the UTM7305 electronic pressure testing machine) with reference to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is weighed and added to a container with a bottom area of ​​1.327 cm 2 In the mold, pressurize to the required pressure, maintain the pressure for 30 seconds, release the pressure, maintain for 10 seconds, and then record and calculate the powder compaction density of the material under the required pressure.

[0064] In this disclosure, the term "degree of graphitization" has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an X-ray diffractometer (such as a Bruker D8 Discover). The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d002 of the C(002) plane in the material's crystal structure, and then calculated according to the formula g = (0.344-d002) / (0.344-0.3354)×100%. Wherein, d002 is the average interlayer spacing of the C(002) plane in the material's crystal structure expressed in nanometers (nm).

[0065] For systems with higher energy density requirements, thick coatings are often used, requiring a high electrode density, which hinders ion transport and negatively impacts the low-temperature fast-charging performance of secondary batteries. Therefore, how to achieve both high energy density and good low-temperature fast-charging performance in high-energy density batteries is a pressing technical challenge.

[0066] As an important component of secondary batteries, the performance of the negative electrode is crucial to the performance of secondary batteries.

[0067] In view of this, the inventors cleverly improved the structure of the negative electrode film layer, which enables the secondary battery to have both high energy density and good low-temperature fast charging performance.

[0068] Based on this, the present disclosure proposes a secondary battery.

[0069] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack.

[0070] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0071] The secondary battery provided in the first aspect of the present disclosure includes the negative electrode sheet described below.

[0072] [Negative electrode]

[0073] The negative electrode sheet disclosed herein includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector; the negative electrode film layer includes a lower region and an upper region, the lower region includes a first negative electrode active material, and the upper region includes a second negative electrode active material; wherein the second negative electrode active material includes both primary particles of carbon material and secondary particles of carbon material, and the volume distribution particle size Dv50 of the second negative electrode active material is less than or equal to 13 μm.

[0074] The above technical solution is to use two carbon materials (i.e., primary particle carbon material and secondary particle carbon material) in the negative electrode film layer area away from the negative electrode current collector (i.e., the upper area) for combined use. The granulation structure of the secondary particle carbon material is conducive to reducing the OI value of the material and is conducive to low-temperature fast charging performance. At the same time, the single particle carbon material (i.e., primary particle) is conducive to increasing the active specific surface area, reducing the charge transfer resistance (Rct), and further improving the low-temperature fast charging performance of the battery. In addition, by matching different granular carbon materials, the volume distribution particle size D of the second negative electrode active material is made V 50 is less than or equal to 13μm, so that the upper area of ​​the electrode has a better pore distribution state, which is beneficial to improving the transmission performance of ions and electrons and further improving the low-temperature fast charging performance.

[0075] In some embodiments, the volume distribution particle size D of the second negative electrode active material is V 50 is 8 μm to 13 μm. The volume distribution particle size D of the second negative electrode active material V 50 Within the above range, it is more conducive to forming a better pore distribution state in the upper area of ​​the electrode, which is more conducive to improving the transmission performance of ions and electrons and improving the low-temperature fast charging performance of the battery.

[0076] In some embodiments, the volume distribution particle size D of the carbon material of the primary particles is V50 is smaller than the volume distribution particle size D of the carbon material of the secondary particles V 50. The above technical solution comprises a carbon material with smaller primary particles and a carbon material with larger secondary particles in the negative electrode film region away from the negative electrode current collector. The granulation structure of the larger secondary particles is more conducive to reducing the OI value of the material, which is beneficial to low-temperature fast charging performance. At the same time, the carbon material mixed with smaller primary particles is more conducive to the active specific surface area, further improving the low-temperature fast charging performance of the battery.

[0077] In some embodiments, the volume distribution particle size D of the carbon material of the primary particles is V In some embodiments, the volume distribution particle size D of the carbon material of the primary particles is 3.5 μm to 6 μm. V In some embodiments, the volume distribution particle size D of the carbon material of the secondary particles is 3.5 μm to 5.0 μm. V 50 is 10.0 μm to 14.0 μm. In some embodiments, the volume distribution particle size D of the carbon material of the secondary particles is V 50 is 10.0μm to 13.5μm. Through the selection and combination of the reasonable particle sizes of the primary and secondary carbon materials, the upper area of ​​the membrane layer has good porosity, ensuring the lithium ion transmission channel and further improving the low-temperature fast charging performance.

[0078] In some embodiments, the powder OI value of the carbon material of the primary particles is greater than the powder OI value of the carbon material of the secondary particles. In some embodiments, the powder OI value of the carbon material of the primary particles is 3 to 6. In some embodiments, the powder OI value of the carbon material of the secondary particles is 2 to 5.

[0079] Through the above design, the material particles have ion embedding ports in all directions, which can quickly receive ions from the positive electrode, thereby further improving the low-temperature fast charging performance of the secondary battery.

[0080] In some embodiments, the specific surface area of ​​the carbon material of the primary particles is greater than that of the carbon material of the secondary particles. By increasing the specific surface area of ​​the carbon material of the primary particles to be greater than that of the carbon material of the secondary particles, it is more advantageous to maintain the proportion of active specific surface area in the upper region of the membrane layer, thereby improving the low-temperature fast-charging performance of the battery.

[0081] In some embodiments, the specific surface area of ​​the carbon material of the primary particles is 2.0 m 2 / g to 3.5m 2 In some embodiments, the specific surface area of ​​the carbon material of the primary particles is 2.0 m 2 / g to 3.2m2 In some embodiments, the specific surface area of ​​the carbon material of the secondary particles is 0.6 m 2 / g to 1.5m 2 In some embodiments, the specific surface area of ​​the carbon material of the secondary particles can be 0.6 m 2 / g to 1.2m 2 Therefore, when the specific surface area of ​​the carbon material is within the above-mentioned range, the ion embedding channel in the upper region of the membrane layer can be maintained, promoting the rapid diffusion of ions from the particle surface to the bulk phase.

[0082] In some embodiments, the carbon material of the primary particles satisfies: the volume distribution particle size D of the carbon material of the primary particles V When the volume distribution particle size Dv10 of the primary carbon material particles is within the above range, it is beneficial to improve the transport performance of ions and electrons, thereby further improving the fast charging performance of the secondary battery.

[0083] In some embodiments, the carbon material of the primary particles satisfies: the volume distribution particle size D of the carbon material of the primary particles V When the volume distribution particle size Dv90 of the primary particles of the carbon material is within the above range, the particles have good consistency, which is beneficial to improving the transmission performance of ions and electrons.

[0084] In some embodiments, the carbon material of the primary particles satisfies: the particle size distribution (D V 90-D V 10) / D V 50 is 1.1 to 1.8. The particle size distribution of the primary particles of the carbon material (D V 90-D V 10) / D V 50 is within this range, indicating that the carbon material is well distributed, which is beneficial for the upper region of the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and further improving the fast charging performance of the secondary battery.

[0085] In some embodiments, the carbon material of the primary particles satisfies: the tap density of the carbon material of the primary particles is 0.8 g / cm 3 to 1.1 g / cm 3 When the tap density is within the above range, the compaction density of the negative electrode film layer can be increased, thereby achieving low-temperature fast charging performance while taking into account the energy density of the battery.

[0086] In some embodiments, the carbon material of the primary particles satisfies the following conditions: the powder compaction density of the carbon material of the primary particles at 20,000 N is 1.35 g / cm 3 Up to 1.55g / cm 3 When the powder compaction density is within the above range, the compaction density of the negative electrode film layer can be increased, thereby achieving low-temperature fast charging performance while taking into account the energy density of the battery.

[0087] In some embodiments, the carbon material of the primary particles satisfies the following conditions: the degree of graphitization of the carbon material of the primary particles is 90% to 93%. When the degree of graphitization of the carbon material of the primary particles is within this range, it is beneficial to improve the ion transport performance of the negative electrode film layer, thereby enabling the secondary battery to achieve both high energy density and good fast charging performance.

[0088] In some embodiments, the carbon material of the secondary particles satisfies: the volume distribution particle size D of the carbon material of the secondary particles V 10 is 4.5 μm to 8.0 μm. Volume distribution particle size D of the secondary particles of carbon material V Within this range, the carbon material is beneficial to the matching of the carbon material with the carbon material of the primary particles, thereby being beneficial to the compaction density and further contributing to the energy density of the battery.

[0089] In some embodiments, the carbon material of the secondary particles satisfies: the volume distribution particle size D of the carbon material of the secondary particles V 90 is 18μm to 24μm.

[0090] In some embodiments, the carbon material of the secondary particles satisfies: the particle size distribution (D V 90-D V 10) / D V 50 is 0.9 to 1.3. The particle size distribution of the carbon material of the secondary particles (D V 90-D V 10) / D V 50 Within this range, it indicates that the carbon material is well distributed, which is conducive to the upper region of the negative electrode film layer having a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and further improving the fast charging performance of the secondary battery.

[0091] In some embodiments, the carbon material of the secondary particles satisfies: the tap density of the carbon material of the secondary particles is 0.9 g / cm 3 to 1.2g / cm 3 When the tap density is within the above range, it can cooperate well with the primary particles to improve the compaction density of the negative electrode film layer, thereby achieving low-temperature fast charging performance while taking into account the energy density of the battery.

[0092] In some embodiments, the carbon material of the secondary particles satisfies the following conditions: the powder compaction density of the carbon material of the secondary particles at 20,000 N is 1.55 g / cm 3 to 1.70g / cm 3 When the compaction density of the carbon material powder of the secondary particles is within the above range, it can cooperate well with the primary particles to improve the compaction density of the negative electrode film layer, thereby achieving low-temperature fast charging performance while taking into account the energy density of the battery.

[0093] In some embodiments, the carbon material of the secondary particles satisfies the following conditions: the degree of graphitization of the carbon material of the secondary particles is 92% to 95%, thereby facilitating the secondary battery to have both high energy density and good fast charging performance.

[0094] In some embodiments, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the primary particles is less than the mass proportion of the carbon material of the secondary particles; optionally, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the primary particles is 20% to 40%; optionally, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the secondary particles is 60% to 80%.

[0095] By setting the mass proportion of the carbon material of the primary particles to be smaller than the mass proportion of the carbon material of the secondary particles, it is beneficial to improve the low-temperature fast charging performance of the battery while taking into account the energy density.

[0096] In some embodiments, the carbon material of the primary particles and / or the carbon material of the secondary particles is artificial graphite.

[0097] In some embodiments, the first negative electrode active material includes artificial graphite and / or natural graphite; alternatively, the first negative electrode active material includes both artificial graphite and natural graphite.

[0098] In some embodiments, the first negative electrode active material comprises natural graphite, and the volume distribution particle size D of the natural graphite is V 50 is 9 μm to 20 μm. The first negative electrode active material includes natural graphite, wherein the abundant coating layer on the surface of the natural graphite and the internal pore structure are further beneficial to low-temperature fast charging performance, and the gram capacity of the natural graphite in the lower region is higher than the capacity of the carbon material in the upper region, which is beneficial to meeting the requirements of energy density.

[0099] In some embodiments, the first negative active material includes secondary particles of artificial graphite.

[0100] In some embodiments, the first negative electrode active material comprises artificial graphite, and the volume distribution particle size D of the artificial graphite isV 50 is 12μm to 17μm, optionally 13μm to 16μm.

[0101] In some embodiments, the first negative electrode active material comprises natural graphite. In some embodiments, the volume distribution particle size D of the natural graphite is V 10 is 5.0 μm to 12.0 μm. In some embodiments, the volume distribution particle size D of the natural graphite V 90 is 20 μm to 30 μm. In some embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is 0.9 to 1.3. In some embodiments, the tap density of the natural graphite is 0.9 g / cm 3 to 1.2g / cm 3 In some embodiments, the natural graphite has a powder compaction density of 1.60 g / cm2 at 20,000 N. 3 to 1.90g / cm 3 In some embodiments, the degree of graphitization of the natural graphite is 96% to 98%.

[0102] In some embodiments, the first negative electrode active material comprises artificial graphite. In some embodiments, the volume distribution particle size D of the artificial graphite is V 10 is 4 μm to 8 μm. In some embodiments, the volume distribution particle size D of the artificial graphite is V 90 is 25 μm to 40 μm. In some embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is 1.0 to 1.4. In some embodiments, the tap density of the artificial graphite is 0.95 g / cm 3 Up to 1.25g / cm 3 In some embodiments, the powder compaction density of the artificial graphite at 20,000 N is 1.70 g / cm 3 to 1.90g / cm 3 In some embodiments, the degree of graphitization of the artificial graphite is 93% to 95%.

[0103] It should be noted that the various parameter tests on the first negative electrode active material, the second negative electrode active material or the negative electrode film layer can be performed by sampling and testing the prepared secondary battery according to the following steps.

[0104] Discharge the secondary battery (for safety reasons, the secondary battery is generally in a fully discharged state); disassemble the secondary battery, take out the negative electrode sheet, and soak the negative electrode sheet in dimethyl carbonate for a certain period of time (for example, 2 hours to 10 hours); then take out the negative electrode sheet and dry it at a certain temperature and time (for example, 60°C, more than 4 hours); then take out the negative electrode sheet.

[0105] Subsequently, the dried negative electrode sheet is baked at a certain temperature and time (for example, 400°C, for more than 2 hours), and an area of ​​the baked negative electrode sheet is selected, and the powder scraped off from the upper 1 / 3 thickness of the film layer is used as the second negative electrode active material, and the powder scraped off from the 1 / 3 thickness of the film layer close to the copper foil is used as the first negative electrode active material; the collected first negative electrode active material and second negative electrode active material are sieved respectively, and finally the first negative electrode active material and second negative electrode active material samples are obtained, which can be used to test the various material parameters mentioned above in the present disclosure.

[0106] As an example, the test method for the volume distribution particle size Dv50 of the second negative electrode active material can be: the sample is dispersed in a suitable liquid (for example, deionized water) or gas at an appropriate concentration by ultrasonic treatment or the like, and is measured using a laser particle size analyzer (such as the Malvern Master Size 3000): the sample is passed through a monochromatic light beam (usually a laser), and when the light encounters the particles, it is scattered at different angles. The scattered light is measured by a multi-element detector, and these values ​​related to the scattering pattern are stored and used for subsequent analysis. Through appropriate optical models and mathematical processes, these quantitative scattering data are converted to obtain the percentage of the particle volume on a series of discrete particle size segments relative to the total volume of the particles, thereby obtaining the particle size volume distribution. Among them, the Dv50 particle size represents the particle size corresponding to when the cumulative volume distribution percentage of the particles reaches 50% from the small particle size side in the particle size distribution.

[0107] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0109] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0111] [Method for preparing negative electrode sheet]

[0112] The present disclosure also provides a method for preparing the negative electrode sheet of the present disclosure. The method comprises the following steps:

[0113] A first slurry containing a first negative electrode active material and a second slurry containing a second negative electrode active material are provided; the first slurry is coated on a negative electrode current collector, and then the second slurry is coated, followed by drying and cold pressing to obtain a negative electrode sheet.

[0114] In some embodiments, the first negative electrode active material, as well as an optional conductive agent, an optional binder, and other optional auxiliary agents, may be dispersed in a solvent (eg, NMP) to form a first slurry.

[0115] In some embodiments, the second active material and optional conductive agent, optional binder and other optional auxiliary agents can be dispersed in a solvent (such as NMP) to form a second slurry, wherein the second negative electrode active material includes both primary particles of carbon material and secondary particles of carbon material.

[0116] The first slurry and the second slurry can be applied simultaneously in one application or in two applications. In some embodiments, the first slurry and the second slurry are applied simultaneously in one application. Applying the first slurry and the second slurry simultaneously in one application can reduce the negative electrode film resistance, thereby further improving the rate performance and cycle performance of the secondary battery.

[0117] The coating weight of the first slurry and the second slurry can be adjusted according to actual conditions.

[0118] The first negative electrode active material, the second negative electrode active material, etc. mentioned above can be obtained commercially, or prepared by the following method disclosed in the present invention.

[0119] In some embodiments, primary carbon material particles can be prepared by crushing and shaping coke raw material, followed by graphitization to obtain primary carbon material particles. Specific examples of coke raw material include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke. The graphitization temperature can be between 2800°C and 3200°C.

[0120] In some embodiments, the secondary particle carbon material can be prepared by crushing and shaping a coke raw material, mixing it with a binder, and granulating it. The resulting material is then graphitized to obtain a carbon-based material containing secondary particles. Specific examples of the coke raw material include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke. The graphitization temperature can be between 2800°C and 3200°C. A specific example of the binder can include asphalt.

[0121] The above preparation process does not include the step of forming a carbon coating layer on the surface of the material. As an example, the carbon coating layer on the surface of the carbon material can be formed by carbonizing an organic carbon source. The organic carbon source can be a carbon-containing material known in the art suitable for coating, for example, one or more of coal tar, petroleum asphalt, phenolic resin, coconut shell, etc.

[0122] [Positive electrode]

[0123] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0124] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0125] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0126] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0127] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this disclosure for positive electrode active materials refer to the material's initial state, i.e., before addition. When a positive electrode active material is used in a battery system, its molar Li content will change over the course of charge and discharge cycles.

[0128] In the list of positive electrode active materials in this disclosure, the molar content of O is only a theoretical value. Oxygen release from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0129] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0130] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0132] [Electrolytes]

[0133] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present disclosure has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0134] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0135] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0136] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0137] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0138] [Isolation film]

[0139] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0140] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0141] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0142] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0143] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0145] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0146] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0147] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0148] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0149] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0150] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] In addition, the present disclosure further provides an electrical device, the electrical device including the secondary battery provided in the present disclosure. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0152] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0153] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0154] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0155] Example

[0156] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0157] Example 1

[0158] A mixed material 1-1 of artificial graphite and natural graphite (relevant parameters are detailed in Table 1, and the mass ratio of the two is 6:4) of the first negative electrode active material, a conductive agent Super P, a thickener CMC, and a binder SBR are mixed in a mass ratio of 96.4:1:1.2:1.4, and deionized water is added as a solvent. The mixture is stirred under the action of a vacuum mixer until the system becomes uniform to obtain a first slurry.

[0159] The second negative electrode active material, a mixed material 2-1 of primary particles of artificial graphite and secondary particles of artificial graphite (relevant parameters are detailed in Table 2), a conductive agent Super P, a thickener CMC, and a binder SBR were mixed in a mass ratio of 96.4:1:1.2:1.4, and deionized water was added as a solvent. The mixture was stirred under the action of a vacuum mixer until the system became uniform to obtain a second slurry.

[0160] The first slurry is evenly coated on the negative electrode current collector copper foil. After drying, the second slurry is coated on the surface of the first slurry. After drying and cold pressing, the negative electrode sheet is obtained. The coating weight of the lower area formed by the first slurry and the upper area formed by the second slurry are "7.6mg / cm 2 ” and “5.1mg / cm 2 ", the thickness of the negative electrode single-layer film (i.e. the thickness of the film coated on one side + the thickness of the copper foil) is 0.077mm.

[0161] LiFePO4, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.4:0.8:1.8, and then the solvent NMP was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.

[0162] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a solvent, and then LiPF6 is dissolved in the above solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0163] A polypropylene film (12 μm thick) is used as an isolation membrane and is placed in order with the positive electrode sheet and the negative electrode sheet prepared above, so that the isolation membrane is located between the positive electrode sheet and the negative electrode sheet to play an isolation role. The electrode assembly is then wound to obtain a secondary battery. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, aging and other processes, a secondary battery is obtained.

[0164] Examples 2-9

[0165] A secondary battery was assembled in the same manner as in Example 1, except that the first negative electrode active material and the second negative electrode active material shown in Table 3 were used.

[0166] Comparative Example 1

[0167] A secondary battery was assembled in the same manner as in Example 1, except that the mixture material 2-8 (Dv50 greater than 13 μm) was used as the second negative electrode active material (see Table 2 for relevant parameters).

[0168] Comparative Example 2

[0169] A secondary battery was assembled in the same manner as in Example 1, except that only the mixture material 2-9 (carbon material containing only secondary particles) was used as the second negative electrode active material (see Table 2 for relevant parameters).

[0170] Comparative Example 3

[0171] A secondary battery was assembled in the same manner as in Example 1, except that only the mixture material 2-10 (carbon material containing only primary particles) was used as the second negative electrode active material (see Table 2 for relevant parameters).

[0172] Table 1: First negative electrode active material

[0173] “ / ” in Table 1 indicates that the item does not exist.

[0174] Table 2: Second negative electrode active material

[0175] Secondary battery performance test

[0176] Low temperature fast charging performance test

[0177] At -10°C, the batteries prepared in the Examples and Comparative Examples were fully charged at x C and fully discharged at 1 C within the SOC range of 20%-50%. After 10 cycles, the batteries were fully charged at x C and disassembled to observe whether lithium deposition occurred on the surface of the negative electrode. If no lithium deposition occurred on the negative electrode surface, the charge rate x C was increased in increments of 0.1 C and the test was repeated until lithium deposition occurred on the negative electrode surface. The test was then stopped. The charge rate at this point, (x-0.1) C, was the maximum charge rate of the battery.

[0178] Table 3 below shows the parameters of the negative electrode sheets and secondary battery performance test results of Examples 1-9 and Comparative Examples 1-3.

[0179] Table 3:

[0180] It can be seen from Table 3 that compared with Comparative Example 1 (Dv50 of the second negative electrode active material is greater than 13), Comparative Example 2 (the second negative electrode active material only uses secondary particles) and Comparative Example 3 (the second negative electrode active material only uses primary particles), in Examples 1-9, the low-temperature fast charging performance of the secondary battery is significantly improved by setting the second negative electrode active material to include primary particles of carbon material and secondary particles of carbon material.

[0181] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film formed on at least one surface of the negative electrode current collector; the negative electrode film comprising a lower region and an upper region, the lower region comprising a first negative electrode active material, and the upper region comprising a second negative electrode active material; in, The second negative electrode active material includes both primary particles of carbon material and secondary particles of carbon material, and the volume distribution particle size D of the second negative electrode active material is V 50 is less than or equal to 13μm.

2. The secondary battery according to claim 1, wherein The volume distribution particle size D of the second negative electrode active material V 50 is 8μm~13μm.

3. The secondary battery according to claim 1 or 2, wherein The volume distribution particle size D of the carbon material of the primary particles V 50 is smaller than the volume distribution particle size D of the carbon material of the secondary particles V 50; Optionally, the volume distribution particle size D of the carbon material of the primary particles is V 50 is 3.5μm to 6μm, and more preferably 3.5μm to 5.0μm; Optionally, the volume distribution particle size D of the carbon material of the secondary particles is V 50 is 10.0 μm to 14.0 μm, and more preferably 10.0 μm to 13.5 μm.

4. The secondary battery according to any one of claims 1 to 3, wherein The powder OI value of the carbon material of the primary particles is greater than the powder OI value of the carbon material of the secondary particles; Optionally, the powder OI value of the carbon material of the primary particles is 3 to 6; Optionally, the powder OI value of the carbon material of the secondary particles is 2 to 5.

5. The secondary battery according to any one of claims 1 to 4, wherein The specific surface area of ​​the carbon material of the primary particles is greater than the specific surface area of ​​the carbon material of the secondary particles; Optionally, the specific surface area of ​​the carbon material of the primary particles is 2.0 m 2 / g to 3.5m 2 / g, 2.0m is optional 2 / g to 3.2m 2 / g; Optionally, the specific surface area of ​​the carbon material of the secondary particles is 0.6 m 2 / g to 1.5m 2 / g, optional 0.6m 2 / g to 1.2m 2 / g.

6. The secondary battery according to any one of claims 1 to 5, wherein The carbon material of the primary particles further satisfies at least one of the following (1) to (6): (1) Volume distribution particle size D of the primary particles of the carbon material V 10 is 1.0 μm to 3.0 μm; (2) Volume distribution particle size D of the primary particles of the carbon material V 90 is 9μm to 12μm; (3) The particle size distribution of the carbon material of the primary particles (D V 90-D V 10) / D V 50 is 1.1 to 1.8; (4) The tap density of the carbon material of the primary particles is 0.8 g / cm 3 to 1.1 g / cm 3 ; (5) The powder compaction density of the carbon material of the primary particles at 20000N is 1.35g / cm 3 Up to 1.55g / cm 3 ; (6) The degree of graphitization of the carbon material of the primary particles is 90% to 93%.

7. The secondary battery according to any one of claims 1 to 6, wherein The carbon material of the secondary particles further satisfies at least one of the following (1) to (6): (1) Volume distribution particle size D of the carbon material of the secondary particles V 10: 4.5 μm to 8.0 μm; (2) Volume distribution particle size D of the carbon material of the secondary particles V 90 is 18μm to 24μm; (3) The particle size distribution of the carbon material of the secondary particles (D V 90-D V 10) / D V 50 is 0.9 to 1.3; (4) The tap density of the carbon material of the secondary particles is 0.9 g / cm 3 to 1.2g / cm 3 ; (5) The powder compaction density of the carbon material of the secondary particles at 20000N is 1.55g / cm 3 to 1.70g / cm 3 ; (6) The degree of graphitization of the carbon material of the secondary particles is 92% to 95%.

8. The secondary battery according to any one of claims 1 to 7, wherein Based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the primary particles is less than the mass proportion of the carbon material of the secondary particles; Optionally, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material of the primary particles is 20% to 40%; Optionally, based on the total mass of the second negative electrode active material, the mass proportion of the carbon material in the secondary particles is 60% to 80%.

9. The secondary battery according to any one of claims 1 to 8, wherein The carbon material of the primary particles and / or the carbon material of the secondary particles is artificial graphite.

10. The secondary battery according to any one of claims 1 to 9, wherein The first negative electrode active material includes artificial graphite and / or natural graphite; Optionally, the first negative electrode active material includes both artificial graphite and natural graphite.

11. The secondary battery according to any one of claims 1 to 10, wherein The first negative electrode active material comprises natural graphite, and the volume distribution particle size D of the natural graphite is V 50 is 9μm to 20μm.

12. The secondary battery according to any one of claims 1 to 11, wherein The first negative electrode active material includes secondary particles of artificial graphite.

13. The secondary battery according to any one of claims 1 to 12, wherein The first negative electrode active material comprises artificial graphite, and the volume distribution particle size D of the artificial graphite is V 50 is 12μm to 17μm, optionally 13μm to 16μm.

14. The secondary battery according to any one of claims 1 to 13, wherein The first negative electrode active material includes natural graphite, and the natural graphite satisfies at least one of the following (1) to (6): (1) Volume distribution particle size D of the natural graphite V 10 is 5.0 μm to 12.0 μm; (2) Volume distribution particle size D of the natural graphite V 90 is 20μm to 30μm; (3) The particle size distribution of the natural graphite (D V 90-D V 10) / D V 50 is 0.9 to 1.3; (4) The tap density of the natural graphite is 0.9 g / cm 3 to 1.2g / cm 3 ; (5) The powder compaction density of the natural graphite at 20000N is 1.60g / cm 3 to 1.90 g / cm 3 ; (6) The degree of graphitization of the natural graphite is 96% to 98%.

15. The secondary battery according to any one of claims 1 to 14, wherein The first negative electrode active material includes artificial graphite, and the artificial graphite satisfies at least one of the following (1) to (6): (1) Volume distribution particle size D of the artificial graphite V 10 is 4μm to 8μm; (2) Volume distribution particle size D of the artificial graphite V 90 is 25μm to 40μm; (3) The particle size distribution of the artificial graphite (D V 90-D V 10) / D V 50 is 1.0 to 1.4; (4) The tap density of the artificial graphite is 0.95 g / cm 3 Up to 1.25g / cm 3 ; (5) The powder compaction density of the artificial graphite at 20000N is 1.70g / cm 3 to 1.90g / cm 3 ; (6) The degree of graphitization of the artificial graphite is 93% to 95%. 16 . An electric device comprising the secondary battery according to claim 1 .

Images